1. Field of the Invention
The present invention relates to a reflection type projector, and more particularly, to a reflection type projector employing birefringent prisms to increase the efficiency of the use of light.
2. Description of the Related Art
A projector is generally known as an apparatus for projecting an image formed by an image forming means using an additional illuminating apparatus.
FIG. 1 shows a conventional reflection type projector. The conventional reflection type projector includes a light source 10 for emitting light, a color wheel 20 for selectively transmitting a predetermined color of an incident light, such as a red, green, or blue color, a scrambler 30 for mixing rays of the incident beam having different degrees of intensity into a uniform beam, a focusing lens 32, a collimating lens 34, a polarization beam splitter (PBS) 40 for changing the proceeding path of an incident beam, a display device 50 for forming an image by selectively reflecting the incident beam, and a projection lens unit 60 for projecting the incident beam onto a screen (not shown).
The light source 10 is comprised of a lamp 11 for generating rays of light, such as a metal haloid lamp or a xenon arc lamp, and a reflecting mirror 13 for reflecting light emitted from the lamp 11 in a proceeding path. The color wheel 20 is installed along the optical path of the light between the light source 10 and the scrambler 30 and can be rotated by a driving motor 21. Red (R), green (G) and blue (B) color filters 22 are arranged on equal areas of the color wheel 20, respectively. The color wheel 20 rotates corresponding to a response speed of a displaying device. Any one of R, G and B of the color wheel 20 is positioned to coincide with the optical path of the light.
The scrambler 30 mixes the incident beam by diffusely reflecting the same such that the rays of the incident beam are changed into rays of uniform light intensity. The focusing lens 32 focuses and diverges the beam having passed through the scrambler 30 such that the diameter of the beam transmitted is enlarged. The collimating lens 34 changes the diverging beam into a parallel beam.
The polarization beam splitter 40 is disposed along the optical path of the light between the collimating lens 34 and the display device 50 and changes a proceeding path of the incident beam by selectively transmitting or reflecting the incident beam at a mirror surface 41 according to a polarization component thereof. That is, the light traveling from the side of the light source 10 is selectively transmitted or reflected depending on whether the polarization component of the beam is a P-polarized beam or an S-polarized beam.
FIG. 1 shows an example in which the beam passing through the polarization beam splitter 40 is used as an effective light. A ferroelectic liquid crystal display (FLCD) of a two dimensional array structure exhibiting a superior response speed is employed as the display device 50. The display device 50 has a plurality of reflection areas of a two dimensional array structure. The reflection areas, each being independently driven, together form an image by modulating polarization directions of the rays of the incident beam.
The beam incident on the display device 50 is reflected again and reenters the polarization beam splitter 40. Here, the beam reentering the polarization beam splitter 40 has a polarization direction which is changed by 90.degree. by the display device 50. Then, the beam is totally reflected by the mirror surface 41 of the polarization beam splitter 40 and proceeds toward the projection lens unit 60. The beam is projected onto the screen via the projection lens unit 60.
However, in the conventional reflection type projector, since a beam of one polarization direction of an incident beam, which is dichotomized depending on the polarization direction thereof, is used as an effective light, efficiency of use of the light is reduced. Also, the reduced light-use efficiency becomes a hindrance in realizing a reflection type projector requiring high brightness.